A tough nut to crack! How to destroy PFOS/PFOA?

A tough nut to crack! How to destroy PFOS/PFOA?
Activated Persulfate Oxidation as a Remediation Technology for
Perfluorooctane Sulfonate and Perfluorooctanoic Acid
Ian Ross (Ph.D.)
Adventus Environmental Solutions Team
Perfluorooctane sulfonate (PFOS) and Perfluorooctanoic acid (PFOA) which can be
generally termed perfluorinated compounds (PFCs) are emerging environmental
pollutants attracting significant attention due to their global distribution, persistence,
toxicity and tendency to bioaccumulate.
There are a number of scientific reports now published reporting that activated
persulfate has the capacity to destroy PFOS and thus there is immense potential for
remediation of PFOS and PFOA impacted soil and groundwater using this versatile
oxidative technology.
Currently hydraulic containment seems to be the only option for PFOS/PFOA impacted
soil and groundwater. However, this article describes potentially robust and versatile
technologies to cause destruction of PFOS/PFOA on site (in situ and/or ex situ), with
the power to alleviate long term liabilities by providing innovative risk management
Fluorinated compounds are classified as being perfluorinated when all the hydrogen
atoms are substituted by fluorine atoms. The structure of PFOS is shown below.
Structure of Perfluorooctane sulfonate (PFOS)
Perfluorinated compounds (PFC’s) have been used extensively in the electronic,
engineering, chemical and medical industries, due to their unique high surface activity,
thermal and acid resistance and both hydro- and lipophobic properties (Lewandowski
et. al., 2006).
PFC’s were nigh production volume chemicals used in a variety of industrial and
consumer applications since the 1950’s and used in the manufacture of leather, paper,
textiles, sealants, paint, semiconductors and aviation hydraulic fuels. PFOS was used in
the production of aqueous film forming foams (AFFFs) for fire fighting activities,
hydraulic aviation fuels and substances used in the chrome plating and photography
industries, so has had a wide array of industrial applications.
Hence there are multiple activities which could result in loss of PFC’s to soil and
groundwater, but one of the more notable uses of PFC’s has been in extinguishing fires,
such that fire fighting activities such as fire fighting training areas can be impacted with
significant concentrations of PFC’s from repeat application of AFFF during multiple
training exercises, or specific fires which extinguish with AFF can lead to a source of
PFC’s is soil and groundwater.
The substitution of hydrogen for fluorine in perfluorinated surfactants contributes to the
persistence of perfluorocarbons relative to hydrocarbon analogues (Key, 1996 and Key
et al., 1997), due to the electronegativity of the fluorine, as well as the overlap between
the 2s and 2p orbitals of fluorine and the corresponding orbitals of carbon. The highly
polarised C-F bond is the strongest known covalent bond, and fluorination usually also
strengthens the adjacent C-C bonds (Kissa, 1994; Hudlicky & Pavlath, 1995). This
means that PFOS is highly persistent, and difficult to degrade.
Therefore, PFC’s are extremely stable and are considered almost un-degradable by
nature (Key et al., 1997) with the only report of reductive defluorination by OchoaHerrera et al. (2008), and their results show Ti(III) citrate successfully defluorinating
PFOS, but the reaction kinetics are slow.
PFOS meets the EU “Persistent‟ and “Very Persistent‟ criteria. It is of note that no
degradation of PFOS by hydrolysis, photolysis or biodegradation has been observed in
any environmental condition tested, as described by the OECD (OECD 2002).
Toxiciological studies examining PFC’s have suggested neurotoxic and immunotoxic
effects (Johansson et al., 2009, Liu et. al., 2010). A recent study by researchers at the
University of California, Los Angeles (UCLA) has found that women who took longer to
become pregnant were more likely to have higher blood levels of PFOS and PFOA
(Potera ,2009).
During the Buncefield fire in the UK in 2005 a significant amount of PFC foam was used
to extinguish the flames, which lead to the collection of immense volumes toxic firewater
which required treating (Sample, 2006). The PFC components of the waste water
represented the most significant challenge as compared to the hydrocarbons which are
amenable to biodegradation.
The key features of these PFCs include:
Extremely persistent
Soil, groundwater, sediment and surface water are key environmental
High water solubility (PFOS solubility 570 mg/L) but bioaccumulative and able to
partition into organic matter (i.e. soils and sediments)
Therefore, innovative solutions to cause destruction of PFOS/PFOA in wastewater, soil ,
sediment and groundwater have been researched over the last few years. Some of the
more successful technologies are described below.
Oxidation of PFOS/PFOA
There are a number of reports showing that oxidation with activated persulfate is
effective for destruction and mineralization of PFOS/PFOA. The versatility of the
activation methodologies should make activated persulfate ideal for in situ and/or ex situ
remediation of PFOS / PFOA impacted soils, sediments and groundwater, however only
laboratory based trials have been reported to date.
Advanced oxidation processes using activated persulfate are characterized by the high
reactivity of the sulfate (SO4 ) and hydroxyl radicals (OH ) in driving oxidation
Several different variation of oxidation processes such as Fenton’s reagents and
persulfate (S2O82-)have been tested and show the most promising results in degrading
PFOS/PFOA (Hori et al., 2005, 2008).
Hori et al. (2005) found that use of persulfate produced highly oxidative sulfate radical
anion (SO4-), which efficiently degrades PFOA to F- and CO2 as major products, whilst
minor amounts of shorter chain perfluorocarboxylic acids (PFCA’s) were formed,
indicating further oxidation would cause complete mineralization. Hori et al., reported
that PFOA at a concentration of 1.35 mM was completely decomposed by a light
activated persulfate system with 50 mM S2O82- and 4 hours of irradiation.
Further work (Hori et al., 2008) showed that heat activated persulfate could effectively
decompose PFOA, as when an aqueous solution containing perfluorooctanoic acid
(PFOA, 374 μM) and S2O82- (50.0 mM) was heated at 80 °C for 6 h. PFOA
concentration in the aqueous phase fell below 1.52 μM (detection limit), and the yields
of F- ions [i.e., (moles of F- formed) /(moles of fluorine content in initial PFOA)] and CO2
[i.e, (moles of CO2 formed) /(moles of carbon content in initial PFOA) ] were 77.5% and
70.2%, respectively, demonstrating significant mineralization of PFOA.
Further to these reports, Lee et al.., 2010 demonstrated that persulfate could be
activated using iron at heat to cause decomposition of PFOA.
Kingshott (2008) assessed differing methods to activate persulfate to treat PFOS, but
adapted methodologies to use persulfate activation methods which can be used more
easily to treat contaminated soils, sediments and groundwater. Treatments that can
most successfully destroy PFOS including Fenton’s reagent, Fenton’s reagent activated
persulfate, H2O2 activated persulfate and heat activated persulfate, all of which showed
>97.5% PFOS destruction.
Some evaluation of strong reductants was also attempted, but this further work using
reduction by sodium dithionite and sodium hypophosphate resulted in incomplete
degradation of PFOS. Some of the results from this research work are shown below.
Review of available studies show that oxidation based technologies such as activated
persulfate and Fenton’s reagent have huge potential to treat PFOS/PFOA impacted soil
and groundwater. However, more in depth bench studies and pilot test are needed
before active application of these technologies in field.
Scale up from laboratory tests to a site pilot are required to allow confidence to develop
in application of oxidants for on site destruction of PFC’s.
Oxidation technologies represent a giant leap forward in managing the risks posed from
PFC’s including PFOS and PFOA.
Hori, H., Yamamoto, A., Hayakawa, E., Taniyasu, S., Yamashita, N. and Kutsuna, S. (2005) Efficient
decomposition of environmentally persistent perfluorocarboxylic acids by use of persulfate as a
photochemical oxidant, Environ. Sci. Technol., vol. 39, no. 7, pp. 2383- 2388.
Hori, H., Nagaoka Y., Murayama M. and Kutsuna S. (2008) Efficient Decomposition of
Perfluorocarboxylic Acids and Alternative Fluorochemical Surfactants in Hot Water, Environ. Sci.
Technol, 42, 7438–7443
Hudlicky, M. & Pavlath, A. E. (1995), Chemistry of Organic Fluorine Compounds II: A Critical Review,
Washington, DC: American Chemical Society
Johansson N., P. Eriksson, H. Viberg, (2009) Neonatal exposure to PFOS and PFOA in mice results in
changes in proteins which are important for neuronal growth and synaptogenesis in the developing
brain, Toxicol. Sci. 108 412-418
Key, B. D. (1996), Ph.D. Dissertation, Michigan State University.
Key, B.L. Howell, R.D. Criddle C.S.1997 Fluorinated organics in the biosphere. Environ Sci. Technol.
31, 2445-2454
Kingshott, L. M. (2008) Remedial Approaches for Perfluorooctane Sulfonate, IMPERIAL COLLEGE
LONDON, Faculty of Natural Sciences , Centre for Environmental Policy , A report submitted in
partial fulfilment of the requirements for the MSc and/or the DIC
Kissa, E. (1994), Fluorinated surfactants: Synthesis, properties, and applications, New York: Marcel
Lewandowski, G., E. Meissner, E. Milchert, 2006 Special applications of fluorinated organic
compounds, J. Hazar. Mater 136, 385-391
Ochoa-Herrera, V., Sierra-Alvarez, R., Somogyi, A., Jacobsen, N.E., Wysocki, V.H. and Field, J.A.
(2008), Reductive Defluorination of Perfluorooctane Sulfonate, Environ. Sci. & Tech, vol. 42, no. 9,
pp. 3260-3264.
OECD (2002), Co-Operation on Existing Chemicals Hazard Assessment Of Perfluorooctane Sulfonate
(PFOS) And Its Salts, Environment Directorate Joint Meeting of the Chemicals Committe and the
Working Party on Chemicals, Pesticides and Biothechnology, Organisation for Economic Cooperation and Development, Paris, 21 November, [Internet] Available:
http://www.oecd.org/dataoecd/23/18/2382880.pdf [Accessed: 16/12/11].
Lee, Yu-Chi, Shang-Lien Lo, Pei-Te Chiueh, Yau-Hsuan Liou, Man-Li Chen 2010 Microwavehydrothermal decomposition of perfluorooctanoic acid in water by iron-activated persulfate
oxidation. Water Research 44, 886-892
Liu C.S., C.P. Higgins, F. Wang, K. Shih (2011) Effect of temperature on oxidative transformation of
perfluorooctanoic acid (PFOA) by persulfate activation in water Original Research Article
Separation and Purification Technology, In Press, Corrected Proof, Available online 2 October 2011
Liu W., Lei Xu, Xiao Li, Yi He Jin, Kazuaki Sasaki, Norimitsu Saito, Itaru Sato, and Shuji Tsuda (2011)
Human Nails Analysis as Biomarker of Exposure to Perfluoroalkyl CompoundsEnviron. Sci. Technol.,
2011, 45 (19), pp 8144–8150
Poetera, C. 2009 Environ Health Perspect. 2009 April; 117(4): A148.
(http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2679623/?log$=activity) [Accessed: 16/12/11].
Sample, I. 2006 (The Guardian, Tuesday 7 February 2006
estions) [Accessed: 16/12/11].